In this study we evaluated fibronectin as a marker of endothelial cell injury and antithrombin III as a marker of chronic activation of intravascular coagulation. The aim of the study was to establish to normal trends of plasma antithrombin III and fibronectin in general obstetric population and to determine the value of both in predicting, distinguishing and understanding the pathophysiology of pregnancy induced hypertension. The all cases consisted of 173 pregnant, 19 of them were chronic hypertensive, 45 were pregnancy induced hypertensive and 119 were normotensive at blood sampling. Out of 119 normotensive cases, 109 cases had no adverse outcome during their pregnancy. These cases were used as a control group and for the normal trends of antithrombin III and fibronectin in general obstetric population. Ten out of 119 cases who developed preeclampsia during follow up, 19 cases with chronic hypertension and 45 cases with pregnancy induced hypertension consisted of the study group. In the cases who developed preeclampsia during follow up, the value of plasma fibronectin level (above 95% confidence limit for that gestational week) to predict preeclampsia had 90% sensitivity and 94.4% specificity. In distinguishing hypertensive disorders of pregnancy (chronic hypertension or pregnancy induced hypertension) fibronectin had 71.1% sensitivity and 100% specificity. Plasma antithrombin III level (of antigenicity) measured by immundiffusion method had no value in predicting and distinguishing pregnancy induced hypertension.